The present invention relates to an apparatus for performing chemical mechanical polishing (CMP) during manufacture of a semiconductor device on a semiconductor substrate. The present invention has particular applicability to monitoring CMP to ensure process quality.
Chemical mechanical polishing (CMP) is a conventional semiconductor device manufacturing technique employed to flatten films, such as interlayer insulating films, and to form metal plugs and interconnections in multiple-layer interconnection processes. As shown in FIG. 1, in a typical CMP apparatus, a rotating holder 12 supports a wafer 14, while a rotating platen 11 holds a polishing pad 17, usually via an adhesive. A first supply nozzle 15 drips a polishing solution in the form of an abrasive slurry onto polishing pad 17, and a second supply nozzle 16 drips water onto polishing pad 17 for rinsing. Typically, pad 17 is larger than wafer 14 (e.g., pad 17 has a 10-inch radius and wafer 14 has an 8-inch diameter), and the wafer and pad are rotated in the same direction at the same speed while they are urged against each other, to effect polishing of wafer 14. Additionally, wafer 14 is typically moved across pad 17 during polishing, but kept away from the center of pad 17 to avoid unwanted torque effects and uneven polishing. As a result, the footprint of polishing pad 17 on wafer 14 during polishing is equivalent to a belt, and the same amount of material is removed across the surface of wafer 14.
As wafer 14 is swept across pad 17 during polishing, some portions of pad 17 may wear to a greater extent than other portions of pad 17. Pad wear is also affected by xe2x80x9cconditioningxe2x80x9d of the pad, a procedure wherein the polishing pad surface is restored to an abrasive condition after being glazed (i.e., made smoother and less abrasive) by normal use. The unevenness of pad wear is expressed graphically in FIG. 2 as a xe2x80x9cwear gradientxe2x80x9d line W1. Depending on the conditioning of the pad, wear is likely to be non-uniform; e.g., pad wear may increase towards the outer radius of pad 17, while the center may not wear at all. This is in contrast to the ideal wear gradient W2, which is even across the pad. Disadvantageously, if pad 17 is worn unevenly, whether due to polishing or conditioning, wafer 14 will see a pressure gradient across pad 17 (e.g., less pressure or xe2x80x9cloadxe2x80x9d towards the edge of pad 17), resulting in less polishing at the edge of pad 17, and uneven polishing of the wafer surface. Moreover, even if the CMP process parameters are optimized so pad wear is even, the rate of wear changes from pad to pad. Thus, it is desirable for process control purposes to monitor pad thickness in situ.
Prior art techniques for monitoring the condition of CMP polishing pads include removing the pad from the platen, cutting a strip from the pad, and measuring its thickness. A more advanced, non-destructive pad testing methodology comprises running a stylus across the polishing pad while it is attached to the platen to measure the pad""s thickness. This method requires that the stylus be stably mounted relative to the pad and platen, and requires that the stylus run across the pad in a reproducible manner, since the stylus must be run across the pad before polishing, and again after polishing, and its measurements compared. However, the reproducibility necessary for accurate measurements can be difficult to achieve. During polishing, the pad is abraded, exposed to the slurry and exposed to water, resulting in different frictional properties across the pad that cause the stylus to rock and produce inconsistent measurements. Furthermore, the relatively rigid polishing pad is often xe2x80x9cstackedxe2x80x9d with a compliant foam underlayer between the pad and the platen. The underlayer can swell during operation as it absorbs liquids such as water and/or slurry, and can become compressed during polishing due to the pressure applied between the pad and the wafer, thereby adversely affecting the accuracy of pad thickness measurements.
An improved methodology for inspecting pad wear is disclosed in copending U.S. application Ser. No. 09/338,357, filed Jun. 22, 1999, wherein a pad wear profile is generated using a contactless displacement sensor, such as a laser displacement sensor. The method of the copending application solves some of the problems inherent in stylus-type pad measurement techniques; however, the measuring apparatus must still be stably mounted relative to the pad, and reproducibility of measurements is still problematic due to stacking of the pad on a compliant underlayer.
As semiconductor devices become more complex and process windows shrink, the need for in-process monitoring of manufacturing techniques such as CMP has become increasingly critical. There exists a need for a simplified, accurate methodology for monitoring CMP pad wear and pad wear profile, thereby reducing manufacturing costs and increasing production throughput.
An aspect of the present invention is a simplified method of monitoring pad wear, pad profile and pad wear profile that does not depend on location of the pad or location of the measuring device for accuracy.
Additional aspects and other features of the present invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the invention. Aspects of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other aspects are achieved in part by a chemical mechanical polishing pad having a plurality of reliefs in a main polishing surface for determining wear of the pad.
Another aspect of the present invention is a method for measuring wear of the thickness of a chemical mechanical polishing pad, the method comprising providing a plurality of reliefs in a main polishing surface of the pad, and measuring a distance from the main polishing surface to a bottom surface of the reliefs.
Additional aspects of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.